1. Field of the Invention
This invention relates to power distribution systems, and more particularly to apparatus for monitoring power usage by a plurality of loads connected to a panel board or circuit breaker. The invention utilizes non-contact current sensors wired to the panel board or breaker and a digital signal processor module connected to receive inptus from the current sensor and from each voltage source so as to avoid having to attach a separate meter to each branch circuit to be monitored. The digital signal processor also enables monitoring of power quality as well as energy consumption for each branch circuit.
2. Description of Related Art
In order to audit or monitor energy usage in a more efficient manner, it is often desirable to monitor not only the overall energy usage by a facility, but also power consumption by individual branch circuits, as well as the effect on power quality of loads in the branch circuits. Such individual branch circuit monitoring not only permits billing for energy used, but also can provide an indication of conditions in the branch circuit, and trigger alerts in case individual limits on such parameters as RMS voltage or current, power factors, or harmonic distortion are exceeded. Furthermore, individual branch circuit monitoring permits billing to be extended to take into account low power factors and/or high total harmonic distortion, promoting efficiency by allowing the operator of a facility to determine whether and where capital investment for power quality enhancement equipment would provide the best return on investment.
Presently, monitoring of individual branch circuits in order to measure branch power parameters such as energy usage by a load, and the effects of the load on power factor and total harmonic distortion (THD), requires the installation of individual current sensors encircling and tied to the wire conductors of the branch circuits that the installer connects from the load to the branch circuit breakers. In order to record energy used, a conventional kilowatt-hour meter needs to be attached to each branch circuit. The costs involved in monitoring branch circuit energy usage can be significant for a typical manufacturing facility, in which multiple discrete circuit breakers or power distribution panels each typically service up to 84 branch circuits. When power quality or other parameters are to be taken into account, the costs rapidly become prohibitive due to the need for installation of additional meters.